This application claims the benefit of Korean Patent Application No. 1999-53022, filed on Nov. 26, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to manufacturing liquid crystal display (LCD) devices, and more particularly, to a method for fabricating liquid crystal panels.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) panel has upper and lower substrates and an interposed liquid crystal layer. The upper substrate usually includes common electrodes, while the lower substrate includes switching elements, such as thin film transistors (TFTs), and pixel electrodes.
As the present invention relates to manufacturing liquid crystal display panels, a brief explanation about conventional liquid crystal display manufacturing processes will be helpful. Common electrodes and pixel electrodes are formed on upper and lower substrates, respectively. A seal is then formed on the lower substrate. The upper and lower substrates are then bonded together using the seal such that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate are opposed to each other, and liquid crystal cells are formed. Liquid crystal material is then injected into the cells through injection holes. The injection holes are then sealed. Finally, polarizing films are attached to the outer surfaces of the upper and lower substrates.
In operation, the light passing through the liquid crystal cells is controlled by electric fields that are applied via the pixel and common electrodes. By controlling the electric fields, desired characters or images can be displayed.
While fabricating the various components of a liquid crystal display, such as the thin film transistors or the color filters, typically requires require numerous manufacturing steps, the overall fabrication process is relatively straightforward. FIG. 1 illustrates a typical liquid crystal panel manufacturing process in some detail. An initial step, st1, forms an array of thin film transistors and pixel electrodes over an array or TFT (lower) substrate.
The next step, st2, forms an orientation film over the lower substrate. This involves uniformly depositing a polymer thin film over the lower substrate and then uniformly rubbing the polymer thin film with a fabric. The rubbing process involves rubbing the surface of the polymer thin film so as to orient or align the film. A typical orientation film is an organic thin film such as a polyimide thin film.
The third step, st3, produces a seal pattern on the lower substrate. When the upper and lower substrates are attached, the seal patterns form cell spaces that will receive the liquid crystal material. The seal pattern also prevents the interposed liquid crystal material from leaking out of the completed liquid crystal cell. A screen-print technology is conventionally used to fabricate the seal pattern using a thermosetting resin.
The fourth step, st4, sprays spacers over the lower substrate. The spacers have a definite size and act to maintain a precise and uniform space between the upper and the lower substrates. Accordingly, the spacers are placed with a uniform density on the lower substrate using either a wet spray method, in which case the spacers are mixed in an alcohol and then sprayed, or a dry spray method in which only the spacers are sprayed. The dry spray method itself is divided into a static electric spray method that uses static electricity and a non-electric spray method that uses gas pressure. Since static electricity can be harmful to the liquid crystal, the non-electric spray method is widely used.
The next step, st5, aligns and attaches the color filter substrate (upper substrate) and the TFT substrate (lower substrate) together. The aligning margin, which is less than a few micrometers, is important. If the upper and lower substrates are aligned and attached beyond the aligning margin, light leakage occurs to prevent a good display quality during the operation of the liquid crystal cell.
In the sixth step, st6, the liquid crystal element fabricated through the five steps is cut into individual liquid crystal cells. Conventionally, liquid crystal material was injected into the space between the upper and the lower substrates before the substrates were cut into individual liquid crystal cells. But, as displays become larger, the liquid crystal cells are usually cut first and then the liquid crystal material is injected. The process of cutting typically includes scribing using a diamond pen to form cutting lines on a substrate, and a breaking step that separates the substrate along the scribed lines.
The seventh step, st7, actually injects liquid crystal material into the individual liquid crystal cells. Since each individual liquid crystal cell is many hundred square centimeters in area, but has only a few micrometer gap between plates, a vacuum injection method is effectively and widely used. Generally, injecting the liquid crystal material into the cells takes the longest manufacturing time. Thus, for manufacturing efficiency, it is important to have optimum conditions for vacuum injection.
FIG. 2 shows a conventional vacuum injection process for injecting liquid crystal material into a liquid crystal cell. To inject the liquid crystal material, a liquid crystal cell 2 having an injection hole 4 is placed inside a vacuum apparatus 6. The liquid crystal cell is located over a vessel 8 that contains the liquid crystal material 10. During operation, suction removes air from the vacuum apparatus 6 to create a strong vacuum.
In practice, it is possible for small air bubbles in the liquid crystal material 10 to gradually add together to form a larger air bubble. Such air bubbles can causes problems. Accordingly, before injection, the liquid crystal material should be left under a vacuum of a few mTorr for a sufficient time so that the air bubbles in the liquid crystal material 10 are removed. Conventionally, the vessel 8 containing the liquid crystal material 10 and the liquid crystal cell 2 are all left under this vacuum condition.
One method of injecting the liquid crystal material into a liquid crystal cell is to dip the liquid crystal cell into the tray containing the liquid crystal material. However, the dipping method consumes too much of the liquid crystal material. Another method involves touching (slightly dipping) only the injection hole 4 to the liquid crystal material. Still referring to FIG. 2, in the touch method, after air in the liquid crystal cell 2 and in the liquid crystal material 10 has been removed, the injection hole 4 is slightly dipped into the vessel 8 containing the liquid crystal material 10. At first, the liquid crystal material 10 is injected into the liquid crystal cell 2 by capillary forces. Later, nitrogen gas is introduced into the vacuum apparatus 6. The difference in pressure between the interior and exterior of the liquid crystal cell 2 forces liquid crystal material 10 into the liquid crystal cell 2.
FIG. 3 is a graph illustrating the pressure in the vacuum apparatus 2 with respect to time. During period xe2x80x9cAxe2x80x9d, a vacuum condition is being formed. At the end of period xe2x80x9cAxe2x80x9d the injection hole 4 is dipped into the vessel 8 containing the liquid crystal material 10. During period xe2x80x9cBxe2x80x9d, the liquid crystal molecules are pressure injected into the liquid crystal cell. After the injection of the liquid crystal material is complete, the injection hole 4 is sealed with an epoxy-based sealant that is applied through a dispenser.
However, for large size panels (such as greater than 20-inch panels including a 30 or 40-inch panel), liquid crystal injection using the above-described injection method takes too much time. Moreover, it is difficult to maintain the cell gap during the injection.
Accordingly, the present invention is directed to a liquid crystal display panel fabricating method that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to increase the fabricating rate and yield of the liquid crystal display panel.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The present invention provides for a fabricating method for a liquid crystal display panel, which includes first and second substrates and an interposed liquid crystal layer, the second substrate including common electrodes, and the first substrate including switching elements, such as thin film transistors (TFTs), and pixel electrodes, the fabricating method comprising: preparing the first and second substrates; depositing first and second orientation film, respectively, on the first and second substrates; depositing a liquid crystal material on the first orientation film of the first substrate; forming a seal material on edges of the first substrate; and attaching the first and second substrates.
In the fabricating method, before depositing the liquid crystal material, each of the first and second orientation films is rubbed in a proper direction. The fabricating method further includes heat-treating the liquid crystal material after attaching the first and second substrates.
In another aspect of the present invention, a fabricating method for a liquid crystal display panel having first and second substrates and an interposed liquid crystal layer comprises providing the first and second substrates; forming first and second orientation films on the first and second substrates, respectively; depositing a liquid crystal material on the first orientation film of the first substrate, the liquid crystal material having a viscosity of greater than 100 mm2/sec; forming a seal material at edges of the first substrate; attaching the first and second substrates; and heat-treating the liquid crystal material to activate the liquid crystal and have substantially the same characteristics as a liquid crystal material having a viscosity of 20 to 50 mm2/sec.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.